When a subscriber calls another through a mobile communication network, a terminating exchanger on the network provides the caller with a uniform ringback tone.
Since the ringback tone is same all the time, a caller can not identify a called before the called answers. Furthermore, the uniform ringback tone can not satisfy various subcribers' needs to reveal their individuality.
By the way, various ad methods are being proposed in these days. One of these ad methods is to send an ad sound message to a caller instead of a conventional ringback tone. However, such an ad sound message is chosen unilaterally by a network operating enterprise. If a caller heard such a unilateral ad sound he or she could talk over a mobile telephone with a called for a limited time.
However, the method that an ad sound is provided instead of a conventional ringback tone still has the aforementioned drawbacks. That is, a caller can not identify a called before the called answers and the uniform ringback tone can not satisfy various subcribers' needs to reveal their individuality.